Question

KULL Illustrate the ATP hydrolysis reaction its regeneration and the AG for both reactions. Show where energy is released in each reaction In the boxes below, Allustrate and describe THREE WAYS IN WHICH ATP HYDROLYSIS provides energy in biological systems ccorrit Module Problem 2.15

Answer 1

Answer 1

ATP is hydrolyzed into ADP as per the following reaction:

ATP+H₂O→ADP+P_i+free energy

Hydrolysis of ATP to ADP is reversible. ADP + P_i regenerate ATP from ADP.

ATP synthesis require an input of free energy whereas ATP hydrolysis releases energy.

ADP is combined with a phosphate to form ATP in the following reaction:

ADP+P_i+free energy→ATP+H₂O

The calculated ∆G for the hydrolysis of one mole of ATP into ADP and P_i is −7.3 kcal/mole (−30.5 kJ/mol). However, this is only true under standard conditions, and the ∆G for the hydrolysis of one mole of ATP in a living cell is almost double the value at standard conditions: 14 kcal/mol (−57 kJ/mol).

• The energy released from the hydrolysis of ATP into ADP is used to perform cellular work, usually by coupling the exergonic reaction of ATP hydrolysis with endergonic reactions.
• Sodium-potassium pumps use the energy derived from exergonic ATP hydrolysis to pump sodium and potassium ions across the cell membrane while phosphorylation drives the endergonic reaction

• Answer 2:

BOX 1

• Energy Coupling in Sodium-Potassium Pumps: Sodium-potassium pumps use the energy derived from exergonic ATP hydrolysis to pump sodium and potassium ions across the cell membrane.

  Cells couple the exergonic reaction of ATP hydrolysis with the endergonic reactions of cellular processes. For example, transmembrane ion pumps in nerve cells use the energy from ATP to pump ions across the cell membrane and generate an action potential. The sodium-potassium pump (Na⁺/K⁺ pump) drives sodium out of the cell and potassium into the cell. When ATP is hydrolyzed, it transfers its gamma phosphate to the pump protein in a process called phosphorylation. The Na⁺/K⁺ pump gains the free energy and undergoes a conformational change, allowing it to release three Na⁺ to the outside of the cell. Two extracellular K⁺ ions bind to the protein, causing the protein to change shape again and discharge the phosphate. By donating free energy to the Na⁺/K⁺ pump, phosphorylation drives the endergonic reaction.

BOX 2:

• Energy Coupling in Metabolism

  During cellular metabolic reactions, or the synthesis and breakdown of nutrients, certain molecules must be altered slightly in their conformation to become substrates for the next step in the reaction series. In the very first steps of cellular respiration, glucose is broken down through the process of glycolysis. ATP is required for the phosphorylation of glucose, creating a high-energy but unstable intermediate. This phosphorylation reaction causes a conformational change that allows enzymes to convert the phosphorylated glucose molecule to the phosphorylated sugar fructose. Fructose is a necessary intermediate for glycolysis to move forward. In this example, the exergonic reaction of ATP hydrolysis is coupled with the endergonic reaction of converting glucose for use in the metabolic pathway.

BOX 3:

• ATP in reaction coupling:

• The formation of sucrose requires an input of energy: its ΔG is about +27 KJ/mol, (under standard conditions). ATP hydrolysis has a ΔG around -30.5 KJ/mol under standard conditions, so it can release enough energy for the synthesis of a sucrose molecule: